<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <button>点击发送请求</button>
    <script>
        const btn = document.querySelector("button");
        let isSending = false;
        btn.addEventListener("click",function(){
            if(isSending) xhr.abort();
            const xhr = new XMLHttpRequest();
            isSending = true;
            xhr.open("GET",'http://127.0.0.1:8000/delay');
            xhr.send();
            xhr.onreadystatechange = function(){
                if (xhr.readyState === 4) {
                    isSending = false;
                    if(xhr.status >= 200 && xhr.status < 300) {

                    }
                }
            }
        })
    </script>
</body>
</html>